Pharynx - Anatomy & Physiology

Introduction

Developing Head - Copyright RVC

The pharynx is part of both the respiratory and digestive system. Both systems have entrances to the pharynx but they are separated from each other by the soft palate. During exercise or during respiratory distress, the mouth can be used as an additional opening of the respiratory system and then the oropharynx also becomes an air-way.

The pharynx can be split into different regions- the oropharynx, laryngeal pharynx (sometimes referred to as the oesophageal pharynx) and the nasopharynx.

Nasopharynx Anatomy - Copyright RVC

Structure and Function

The opening of the larynx is on the floor of the pharynx. Caudal and dorsal to the laryngeal opening is the opening into the oesophagus. In the dorsal region of the nasopharynx there are paired openings into the auditory (eustacian) tubes. The lining of the middle ear cavity and auditory tube is continuous with that of the nasopharynx. It is located between the base of the skull and the first two cervical vertebrae dorsally and the larynx ventrally. The mandible, pterygoid muscles and hyoid apparatus are located laterally. Laterally, two pairs of palatopharyngeal arches are present from the soft palate to the oesophagus.

Pharynx Labelled - Copyright C.Clarkson and T.F.Fletcher University of Minnesota

The walls of the pharynx contain striated muscle. During swallowing, the soft palate is raised which divides the pharynx into dorsal and ventral sections. The dorsal compartment is the nasopharynx and the rostral compartment is the oropharynx. The laryngeal pharynx is separated from the oropharynx by the epiglottis. Tonsils are present on the lateral walls of the oropharynx and are covered by flaps of mucosa. It is partially visible in the open mouth.

The pharynx plays an important role in deglutition.

Soft palate dividing the oropharynx and the nasopharynx - Copyright RVC

Musculature

Muscles that constrict

• Run dorsally to roof of pharynx

• Rostral constrictor muscles are the hyopharyngeous, pterygopharyngeous and the palatopharyngeous muscles
  • Originate from the pterygoid region of the skull and the aponeurosis of the soft palate
  • Shorten the pharynx

• Middle constictor muscle is the thyopharyngeous muscle
  • Origniates from the hyoid bone

• Caudal constictor muscles are the cricopharyngeous muscle
  • Originates from the thyroid cartilage of the larynx

Muscles that dilate

• Enclose pharynx laterally and dorsally

• Dilator muscle is the stylopharyngeous muscle

• Originates from the hyoid apparatus

• Widens the rostral pharynx

Muscles that shorten

• The pterygopharyngeal muscle and palatopharyngeal muscle shorten the pharynx

• Enclose pharynx laterally and dorsally

Muscles that close the Pharyngeal Arch

• The palatopharyngeous muscle also closes the pharyngeal arch

Innervation

• Pharyngeal muscles arise from arch 4

• Pharyngeal branch of the vagus nerve (CN X) from the cranial root of the accessory nerve (CN XI)

• Stylopharyngeous muscle comes from arch 3 and is innervated by the accessory nerve (CN XI)
• Glossopharyngeal nerve (CN IX) supplies taste to the pharynx

Histology

Histology of Pharyngeal Tonsil - Copyright RVC

• Fibroelastic aponeurosis supports the mucosa

• nasopharynx has pseudostratified columnar epithelium

• oropharynx and the laryngeal pharynx have stratified squamous epithelium

• oropharynx and the laryngeal pharynx have salivary glands present

Species Differences

Palatine Tonsil - Copyright C.Clarkson and T.F.Fletcher University of Minnesota

Canine

• Single duct connects nasopharynx to the nasal cavity

• Tonsils are a compact mass which point away from the lumen of the pharynx

Equine

• Auditory tube opens into the guttural pouch

• Tonsils are diffuse and raised slightly

• Horses are unable to breathe through the mouth as the free apex of the rostral epiglottis lies dorsal to the soft palate in a normal horse.

Ruminants

• Tonsils are a compact mass which point towards the lumen of the pharynx

Links

Oropharynx - Anatomy & Physiology

Nasopharynx - Anatomy & Physiology

laryngeal pharynx

Test yourself with the Oropharynx, Facial Muscle & Pharynx flashcards

Oropharynx Flashcards

Facial Muscles Flashcards

Pharynx Flashcards

Laryngeal Pharynx Flashcards

Nasal Pharynx Flashcards